Method and apparatus for open pit bench mining

ABSTRACT

A bench mining system and mining method, particularly useful for open pit bench mining, employs a combination of bulldozers and transversely movable apron feeders to provide the primary mechanism for removal of overburden. The apron feeders are preferably equipped with a self-cleaning arrangement to facilitate continuous operation without undue stoppages.

FIELD OF INVENTION

This invention relates to methods and apparatus for mining and inparticular for open pit bench mining and apron feeders used inconnection therewith.

BACKGROUND

In modern mining, geologic surveys and other techniques estimate thesize and shape of mineral and/or ore configurations before their removalin a mining operation. The ore and mineral deposits exist in layers orveins at varying depths below ground. For example, deposits of coal canbe divided into multiple layers of substantially horizontal planes ofvarying thickness and at various depths such that several deposits orveins lie at different levels spanning hundreds of feet below ground.Such layers of mineral and ore deposits are often not completelyhorizontal but have a pitch or slope. Because of the three dimensionalsloping layers, the deposits are generally mined from the shallowest endof the deposit in a down slope direction.

In general the rock and earth disposed on top of a mineral or ore layeris referred to as “overburden”. In open pit mining, the overburden atopa first uppermost layer is removed to substantially expose a strip ofthe mineral or ore deposit. The exposed deposit is then accessible to beremoved by mining the uncovered portion and transporting it from themine for shipment or other processing. Overburden is then removed fromabove a next adjacent strip of the first layer deposit to substantiallyexpose more of the first deposit layer for removal by mining andshipment.

In open pit mining, once a portion of the uppermost deposit layer ismined and removed, the rock that had been sandwiched between theuppermost layer and the and the next lower deposit layer is exposed andis the overburden atop the next lower layer. Accordingly, the open pitprocess mining continues by removing strips of that overburden togenerally expose the next deposit layer, in a sequential process thatcontinues until successive deposit layers are exhausted. Depending onthe size of the deposit, each strip may be several miles in length andis typically about 100 or more feet in width depending on the type ofequipment used for the mining operation and other factors such as thesize and pitch of the deposit layer.

As open pit mining continues, overburden removal above each depositlayer forms steps or benches. At each step, multiple removal operationsincrease efficiency in mining the ore or other minerals within thedeposits. Multiple operations, however, take some time, and can be costprohibitive if projected mining yields are not sufficiently high.

The valuable deposit layers are generally much smaller than the layersof overburden. Thus, the most labor intensive task in open pit mining isthe removal of the overburden.

In one conventional mining method, a bucket wheel excavator 500, asillustrated in FIG. 1A, loads overburden 29 onto dump trucks 180. Asingle bucket wheel excavator 500 may cost on the order of One-HundredMillion Dollars ($100,000,000) and require a trained crew of 6 to 8persons to operate.

As an alternative to a bucket wheel excavator, shovels, drag lines orother bucket type equipment are often used to remove overburden. Forexample, FIG. 1B illustrates a conventional operation where a shovel 502loads large oversized dump trucks 180 which deposit their materials intoa hopper on a centrally located apron feeder 550. The apron feeder 550may feed a sizer that reduces oversized chunks of overburden to a sizemanageable by a conveyor 506 or other means of transport that carriesthe removed overburden away from the active mining area.

In a conventional mining operation, the apron feeders 550 is typicallylocated at a semi-permanent position where overburden is trucked anddeposited to a feed end of the apron feeder. When initially positionedor relocated, an apron feeder 550 is traditionally moved in a directionaligned with the feeder's conveyor operation so that they areessentially backed into a desired location. It is known in the art toprovide apron feeders 552 with wheels or crawler undercarriage in linewith the feeder operation for the purpose of positioning the apronfeeders 552 such as illustrated in FIGS. 2A and 2B.

Applicants have recognized that it would be desirable to provide amethod and system of open pit mining that reduces or eliminates the needfor reliance on complicated and expensive equipment such as bucket wheelexcavators and efficiently uses the necessary equipment. Applicants havein particular recognized that more efficient mining can be conductedthrough the creative expanded use of apron feeders in the miningoperation.

Further, applicants have recognized that improved apron feeder designsmay be employed to prevent costly operational stoppages due to the needfor cleaning clogged material from an apron feeder.

SUMMARY

A bench mining system, mining method and related equipment are providedin which a combination of bulldozers and transversely movable apronfeeders provide a primary mechanism for overburden removal. The mobilityof teams of dozers along with the apron feeder, as described herein, isa significantly new and effective innovation in overburden removal. Withan eye towards being able to move the entire mining operation, not onlyare the earth-moving pieces of equipment considered movable, but so isthe entire infrastructure supporting the earth-moving equipment,including pump-houses, retaining walls, and the like.

In a preferred embodiment, a mining floor or “bench” is defined adjacentto a section of a deposit layer and overburden. Preferably, theoverburden and deposit layer have a combined height relative to thebench of between 50 to 150 feet. An apron feeder is disposed on thebench in front of a pre-blasted section of overburden which preferablyruns about 300 feet along the bench and the apron feeder is preferablypositioned in the approximate center of the 300 feet long section.Selective blasting, as is well known in the art, is used to loosen theoverburden rock and/or other material of which it is composed whileleaving the deposit layer substantially intact. Preferably, the loosenedsection of overburden in front of which the apron feeder is positionedis about 225 feet wide, extending away from the apron feeder.

The invention further comprises bulldozers working in coordinated teamsthat push the overburden of the pre-blasted section onto the feed end ofthe apron feeder by preferably forming a natural hopper and relying ongravity to create a flow of the loosened overburden into the apronfeeder. The bulldozers preferably work in defined zones and coordinatetheir efforts depending on the number of bulldozers employed. The apronfeeder is then used to either load the bulldozed overburden onto trucksor onto a conveyor system for removal from the active mining area. Afteroverburden removal, the substantially uncovered portion of the depositlayer is then mined using conventional methods.

The operation preferably continues along the bench by blasting furthersections of overburden and transversely relocating the apron feeder infront of the next loosened section whereat further bulldozing pushes theloosened overburden into the apron feeder, which in turn, feeds thetrucks or the conveyor system.

Where the layer deposits are in closely spaced intervals of less than 50feet, a bench can be defined adjacent a section having an intermediatedeposit layer within the overburden. In such case, selected blastingtechniques known in the art are employed to blast the overburden atopthe intermediate deposit layer as well as below the intermediate depositlayer. Then the bulldozing operation first removes the upper portion ofoverburden above the intermediate deposit layer and the intermediatedeposit layer is mined and removed. Thereafter, the bulldozers are usedto remove the lower portion of the overburden. The apron feeder can beeither transversely displaced to a location for receiving anothersection of upper loosened overburden while the intermediate depositlayer is mined from the first section or remain at the same location forboth upper and lower overburden removal operations.

Where the layer deposits are spaced at an interval of more than 150feet, a bench can be defined where there is no deposit layer of mineralor ore within the overburden. In such case, after blasting and removalof the loosened overburden by dozing it into the apron feeder, no miningoperation is required on that bench.

The blasting, dozer/apron feeder overburden removal, and deposit miningoperations are preferably contemporaneously conducted on several bencheswhere each operation is selectively transversely spaced from each otherby a selected safety margin.

In order to implement the system and operation thereof, the inventiveapron feeders are preferably provided with a frame that permitsengagement with a crawler for displacement of the apron feeder in adirection that is transverse to a conveying direction of the apronfeeder. Alternatively, the apron feeder is provided with an innovativededicated crawler affixed thereto or other means of transverselocomotion to facilitate efficient operations as the removal ofoverburden proceeds along one of the benches.

Preferably, apron feeders used to conduct the inventive mining operationare provided with a self-cleaning mechanism to facilitate continuousoperation without undue stoppage delays. In particular, the apron feederis preferably provided with a scroll plate at its inlet end to catchoverspill material as the apron feeder is loaded. Preferably, a“grizzly” component is mounted on an apron feeder flight that serves tobreak up and/or loosen material caught by the scroll plate and a wipercomponent is disposed on an apron feeder flight a selected distancebehind the grizzly to clear the material from the scroll by pushing itback to the top of the apron feeder inlet end.

Other objects and advantages of the present invention will be apparentfrom the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1A is a perspective illustration of a prior art bucket wheelexcavator used in conventional open pit mining.

FIG. 1B is a schematic illustration of a conventional open pit miningoperation where a shovel loads short haul dump trucks that transport theshoveled material to a relatively stationary fixed position apron feederin a conventional open pit mining operation.

FIG. 2A illustrates the mobility of a conventional apron feeder in linewith the feeder's conveying operation utilizing a crawler.

FIG. 2B illustrates the mobility of a conventional apron feeder in linewith the feeder's conveying operation utilizing wheels.

FIG. 3A is an overall perspective view of an open pit bench miningsystem in accordance with the teachings of the present invention.

FIG. 3B is a perspective schematic diagram of the mining system of FIG.3A wherein a bench is adjacent to a formation that includes multipledeposit layers.

FIG. 4 is an elevated side view of an apron feeder configured for use inthe mining operation depicted in FIGS. 3A and 3B.

FIG. 5A is an illustration of a preferred apron feeder and transporter.

FIG. 5B is an illustration of a transport tractor.

FIG. 5C is an illustration of a preferred apron feeder with extensionwalls and a sizer attached to the outlet end of the apron feeder.

FIG. 5D is an illustration of an apron feeder with extension walls.

FIG. 5E is an illustration of an alternate embodiment of the transporttractor and apron feeder.

FIG. 6A is an elevated side view of the feed end of an apron feederfitted with a scroll element.

FIG. 6B is a perspective illustration of a self-cleaning mechanism of anapron feeder.

FIG. 6C is a perspective illustration of a top view of a preferred apronfeeder.

FIGS. 7A and 7B are side and top views of an initial push to an apronfeeder.

FIGS. 7C-E show three successive cuts of overburden.

FIG. 8 illustrates a top view of a successive dozer push towards anapron feeder.

FIG. 9 illustrates a top view of a first embodiment of a method ofloading the apron feeder.

FIG. 10 illustrates a top view of a second embodiment of a method ofloading an apron feeder.

FIG. 11 illustrates a top view of a third alternate embodiment of amethod of loading an apron feeder.

FIGS. 12A-H illustrate iterative steps in a top view of a fourth methodfor loading a movable apron feeder.

FIGS. 13A-H illustrate iterative steps in a top view of a fifth methodfor loading a movable apron feeder.

FIG. 14A-I illustrate iterative steps in moving an apron feeder used inthe invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Overview of Operation and Equipment

FIG. 3A illustrates an open pit mining operation 20 wherein threebenches 22, 24, 26 are at different levels relative to deposit layers28, 30, 32 respectively. A layer of overburden 29, 31, 33, which aremoval operation carries away, covers each level of deposit layer 28,30, 32. Once the mineral or ore deposit is exposed, a mining operationremoves the deposit layer 28, 30, 32 for further processing.

Preferably, the benches 22, 24, 26 are defined such that the height H ofthe deposit 28, 30, 32 and overburden 29, 31, 33 to which they areadjacent is between 50 and 150 feet. Each bench itself, preferably has awidth of at least 100 feet extending from the deposit and overburden towhich it is adjacent.

On each bench, an apron feeder is disposed in front of a pre-blastedsection S₁ of loosened overburden 29L, 31L, 33L which preferably has alength L which runs about 300 feet along the bench. The apron feeder ispreferably positioned at the approximate center of the 300 feet longsection S₁. Preferably, the loosened section S₁ of overburden in frontof which the apron feeder is positioned has a width W of about 225,extending away from the apron feeder. With the apron feeder 150 inplace, bulldozers 200 push the loosened overburden 29L, 31L, 33L of thesection S₁ into the feed end 152 of the apron feeder 150 using one ofthe methods shown in FIGS. 7-13, and discussed in more detail below.

The apron feeder 150 conveys the loosened overburden 31L, 33L ontotrucks 180 for removal from the active mining area. Alternatively,loosened overburden 29L is fed into a sizer 185 for removal on aconveyor system 210. After removal of the overburden 29L, 31L, 33L, asubstantially uncovered section D of the deposit layer 28, 30, 32 isthen mined using conventional methods. As a practical matter, trucks arepreferred for the deeper benches, but this is dependent on the type andavailability of conveying equipment to serve as an alternative means.

Selective blasting to loosen the overburden 29, 31, 33 is performedusing techniques well known in the art to loosen the rock and otheroverburden material while leaving the deposit 28, 30, 32 intact. Asecond section S₂ of overburden may be loosened by blasting before theapron feeder/dozer overburden removal operation is conducted. Inpractice, both safety considerations and operational efficiency arepreferably used to determine when and whether multiple sections ofoverburden are to be blasted to loosen the overburden for the overburdenremoval operation.

In accordance with conventional practice, the exposed sections Dresulting from the dozer/apron feeder overburden removal operation willinclude a relatively small overlying buffer layer of rock material sothat the mineral or ore deposit itself is not contaminated by theblasting process. That relatively thin buffer layer is removed usingconventional methods and the mineral or ore is removed by mining in arelatively pure form and is transported out of the open pit mine forfurther processing and/or shipment.

Preferably on each bench 22, 24, 26, the operations continue laterallyalong each bench and can be conducted contemporaneously at spacedlocations on each bench. In general, the blasting overburden operationprecedes the dozer/apron feeder overburden removal operation which inturn precedes the mining of the mineral or ore deposit. Each of theupper benches, such as benches 24 and 26, are in fact defined byoverburden for a lower bench. Accordingly, the blasting of sections ofoverburden 29 is performed after that area has already completed itsservice in forming a base for removal operations of the higheroverburden and mining of the upper deposits.

As illustrated in FIG. 3A, contemporaneous operation of the threeprocedures, blasting, overburden removal and mining, can be laterallyspaced along each bench with the active areas respectively beinglaterally spaced to produce a very efficient mining operation withrelatively inexpensive equipment.

Variations Due to Spacing of Mineral or Ore Deposits

As noted above, the benches are preferably defined such that theadjacent overburden and deposit combination is in a range from 50 to 150feet in height H. Where the layer deposits are spaced in close intervalof less than 50 feet, a bench can be defined where there is anintermediate deposit layer within the overburden.

In such case, selected blasting techniques known in the art are employedto blast the overburden 31 atop the intermediate layer 30 i as well asbelow the intermediate deposit layer. Preferably, a bulldozing operationfirst removes the upper overburden above the intermediate deposit layer,the intermediate deposit layer is mined and removed, and then bulldozersare used to remove the lower portion of the overburden. The apron feedermay be transversely displaced to a location for receiving anothersection of upper loosened overburden and then transversely returned.Alternatively, the apron feeder may remain at the same location duringremoval of the intermediate deposit for both overburden removaloperations.

For example, FIG. 3B illustrates an intermediate deposit layer 30 iwithin the overburden 31 adjacent to bench 24. The intermediate depositlayer 30 i could, for example, be five feet thick having a forty feet ofoverburden all of which is disposed above the lower deposit layer 30that is ten feet thick having forty feet of overburden sandwichedbetween the deposits 30 i, 30. In such an example, the bench 24 isdefined at the level of the lower layer deposit 30 at a depth ofninety-five feet below the top of the overburden of the intermediatedeposit 30 i. After blasting to loosen both portions of the overburden31L in section S₁, bulldozers are then used to first push the upperforty feet of overburden onto the apron feeder 150 stationed therebelowand the five foot thick intermediate deposit 30 i is then removed.Bulldozers then remove the remaining forty feet of overburden lying atopthe lower layer deposit 30 which permits the mining of the lower depositmaterial.

After the overburden atop intermediate deposit 30 i is removed throughthe dozing operation, the apron feeder is preferably transversely movedalong the bench where a next section S₂ of blasted overburden is removedthrough a bulldozing operation while the deposit is removed from thefirst five foot thick upper deposit layer 30 i. Thereafter, thebulldozers and apron feeder can be returned to the first site S₁ toremove the lower forty feet of overburden 31L disposed on the lowerdeposit layer 30.

The return of the apron feeder to finish overburden removal may be afterseveral sections of overburden atop intermediate deposit 30 i areremoved. Alternatively, a second set of dozers and a second apron feedermay be used on the same bench 24 to follow the removal of theintermediate deposit 30 i. The second set of dozers and second apronfeeder would then remove the lower forty feet of overburden to permits asecond mining operation to proceed with respect to removing the lowerdeposit layer 30, preferably using a second set of deposit removalequipment. In either case, the transverse mobility of the apron feedersgreatly facilitates the efficiency of the operation.

Where the layer deposits are spaced at an interval of more than 150feet, a bench can be defined where there is no deposit layer of mineralore within the overburden. In such case, after blasting and removal ofthe loosened overburden by dozing it into the apron feeder, no miningoperation is required on that bench.

The movement of the bulldozers and apron feeders along the benchesallows for efficient removal of both overburden and mineral depositssimultaneously, without extended equipment down time.

Apron Feeder Equipment

As best seen in FIGS. 4, 5A-5E, and 6A-6C, a preferred apron feederassembly 150 is shown which is designed specifically for efficientimplementation of mining operations in accordance with invention byfacilitating transverse apron feeder movement. The apron feeder assemblyincludes a feed end 152, which receives material (overburden) that isconveyed to an outlet end 156 thus defining a conveying direction of thefeeder. The apron feeder 150 is preferably comprised of 180 flights 146,each ten inches wide, which are horizontally pivotally connected in acontinuous loop. This loop defines a conveyor with a top surface 146 athat transports material from the feed end 152 to the outlet end 156 ofthe apron feeder 150, and a bottom surface 146 b. The inlet end 152 ofthe apron feeder is conventionally enclosed within a strong metal box155 called a “dog house” to protect it from impact and from compactedsurrounding material during operation.

The apron feeder 150 is mounted at a desired angle upon a selectivelyconfigured frame 154 such as shown in FIG. 4. The desired angle ispreferably 14 to 15 degrees above horizontal. Preferably, the frame 154supports the apron feeder so that its outlet end 156 is located at aheight sufficient to fill a dump truck 180 positioned beneath the outletend 156. Alternatively, as depicted in FIG. 5C, a sizer 185 can beattached to the outlet end 156 of the apron feeder 150 to reduce largesize chunks of overburden to a manageable size for conveying by aconveyor system 210 which is then disposed beneath a conveyor loadingapparatus 186 associated with the sizer 185.

Where a conveyor system is used, the conveyor system 210 then transportsthe overburden from the active mining site such as illustrated in FIG.1B. As illustrated in FIG. 3A, the conveying system 210 can extend alonga bench 22 so that the entire apron feeder 150 and sizer 185 combinationcan simply move transversely from in front of a section S₁ to asubsequent section S₂ for a highly efficient overburden removal processwithout any alteration to the conveying system. Other alternatives fortransporting overburden material from the apron feeder may be used aloneor in combination with the examples provided above.

The frame 154 preferably includes a selectively defined opening foraccess by a transport crawler 190 in a direction that is transverse tothe conveying direction of the apron feeder 150. As best seen in FIGS.5A, 5B, and 5E, the transport crawler 190 preferably has treads 192 orother motive means suitable for the strip mining environment andpreferably includes a vertically displaceable support bed 194.

In lieu of having a separate crawler 190, the apron feeder assembly 150can include a dedicated transport crawler attached thereto. In Eithercase, the crawler 190 may optionally have a relatively rotatable supportbed 194 associated with the transport crawler 190 to enable the crawlertreads 192 to be turned relative to the apron feeder 150 to be in eithera transverse or an aligned orientation with respect to the conveyingdirection of the apron feeder 150. With such an option, the transportcrawler 190 can move the apron feeder assembly 150 in a conventionalmanner as is done with the apron feeders shown in FIGS. 2A and 2B andalso move the apron feeder assembly 150 in a transverse manner bychanging the directional orientation of the crawler treads.

When the apron feeder assembly 150 is to be relocated on a bench, thetransport crawler 190 preferably travels beneath the apron feederassembly 150 in the space defined by the frame 154, lifts the apronfeeder assembly 150 on the support bed 194 above the bench andtransversely repositions the apron feeder assembly 150 along the benchto a new location where it is lowered onto the bench. Preferably theframe 154 is structured so that the transport crawler 190 engages theapron feeder 150 directly below the center of mass of the entire apronfeeder assembly 150. As shown in FIG. 5C, where the apron feeder 150 isused in connection with the sizer 185, a similar crawler 188 ispreferably provided to transversely relocate the sizer 185 and itsassociated conveyor loading apparatus 186.

As best seen in FIGS. 5C and 5D, the apron feeder assembly 150 ispreferably used in connection with massive extension walls 170, 172 anda hydraulic assembly housing 174 having skids that permit them to bedragged by a bull dozer for placement at a desired location. Unlikeconventional apron feeder walls which are semi-permanently erected suchas illustrated in FIG. 2A, the walls 170, 172 are selectively designedwith a large foot print and sufficient weight to remain immobile duringthe dozing operations used to feed the apron feeder, while remainingsufficiently mobile and easily transportable for quickly establishing asubsequent apron feeder operational site.

The hydraulic assembly housing 174 provides the motive power to theapron feeder and typically includes both hydraulic and electricalequipment for operation the apron feeder. The hydraulic assembly housing174 may be designed with sufficient strength and bulk to serve as one ofthe extension walls. However, it is preferred to provide an extensionwall disposed in between the dozing operations and hydraulic assemblyhousing 174.

As shown in FIG. 5D, preferably, a signal light 176 is provided which iscontrolled by the apron feeder operator having red and green lights. Thesignal light is advantageously used to signal to the operators of thebull dozers which load the apron feeder; a green light indicating whenthe feeder is ready to receive material and a red light indicating noloading should occur. Typically a red light indication will be givenwhen there is a change of trucks at the outlet end.

For apron feeder operation, the walls 170,172 are positioned proximatethe inlet end 152 of the apron feeder 150 and serve to protect the apronfeeder operators and to assist in the formation of the natural hopper 40formed during the dozing operations. The wall 170 also serves to protectthe transport crawler 59 and to keep clear the area beneath the apronfeeder frame 54 for the transport crawler to easily engage the apronfeeder assembly 50 for transport.

Apron Feeder Self-Cleaning Mechanism

The dog box 155 provides protection to the front and sides of the feedend 152 of the apron feeder 150. However, during the dozing operation toload the feeder, some material spills into a gap 162 defined between theapron feeder's feed end 152 and the dog box 155. Although such spillageis a lesser problem when the apron feeder is loaded with dry material,material build up is exponentially increased where the apron feeder isloaded with wet sludge or slurry material. Typically the problem of suchspillage build up results in periodic stoppage of apron feeder operationto remove built up spillage.

As illustrated in FIGS. 6A-6C, in order to prevent or reduce the buildupof overspill material, the apron feeder 150 is provided with a selfcleaning mechanism that includes a spillage catching scroll 140, agrizzly element 142, and a wiper element 144. The scroll element 140comprises a strong metal sheet that is mounted to the dog box at the gap162 and extends substantially parallel to the apron feeder fights 146 infront of the feed end of the feeder for a selected distance parallel thebottom surface 146 b of the feeder 150. Preferably the scroll 140 isapproximately 22 feet long.

The grizzly element 142 is mounted on one of the feeder flights 146 todefine a row of metal teeth spanning transversely across the conveyingsurface. An associated wiper element 144 is mounted on one of the feederflights 146 at a selected distance behind the grizzly 142 to define araised blade spanning transversely across the conveying surface.

In operation, as the apron feeder is loaded, material that spillsthrough the gap 162 is caught by scroll 140 where it collects. With eachcomplete revolution to the apron feeder, the grizzly 142 travels alongthe scroll and breaks up the collected overspill material caught by thescroll. The wiper 144 then follows the grizzly 142 to push the broken upoverspill back up onto the top surface 146 a of the feeder 150. Afterthe wiper 144 passes, the scroll 140 has been cleared to again begin tocatch spillage into the gap 162.

More than one grizzly/wiper set can be provided so that the scroll iscleared multiple times during one complete revolution of the apronfeeder. Preferably, two evenly spaced grizzly/wiper sets are provided,as illustrated in FIGS. 6A and 6B.

Dozer/Apron Feeder Overburden Removal

With reference to FIGS. 7A-7E and 8, details of a preferred dozer/apronfeed overburden removal operation are illustrated. With the apron feeder150 disposed on the bench 22 in front of the loosened section S₁ ofoverburden 29L, the dozers 200 perform an initial push to form a slope34 and natural hopper 40. The dozers push an uppermost layer ofoverburden 29L1 towards the apron feeder 150 to form the slope 34between the overburden section S₁ and the bench 22. The slope 34 anglesdownward to form overburden chute walls 39 on either side of the apronfeeder 150. These chute walls 39 define a natural hopper or chute 40sized and shaped to direct dozer-pushed overburden 29 to the inlet ofthe apron feeder 150.

Once the dozers 200 form the natural chute 40, the dozers 200 begin thetask of removing the overburden 29L proceeds in removal of successivelayers 29L2, 29L3, and 29L4 as illustrated in FIGS. 7C-E. Gravityprovides assistance in this part of the operation since the angle ofrepose of the material being pushed in the natural hopper 40 is suchthat the material naturally slides down the slope 34 to the apron feeder150. However, for the lower most overburden layer 29L4, the dozers 200may need to push the overburden material upward to inlet of the apronfeeder. This is somewhat dependent on the thickness of the underlyingdeposit.

FIGS. 9-14 illustrate several alternative methods for dozing theoverburden 29L into the apron feeder 150. The general objective tomaximize the efficiency of the dozers 200 which generally means to keepthe dozers in constant motion. Accordingly, communication between theapron feeder, supervisors, dozer operators, and other personnel isdesirable to achieve for maximum efficiency.

FIG. 9 shows a first embodiment for dozing loosened overburden 29L in asection S₁ into the apron feeder 150, in which several dozers 200operate in discreet zones 50, 52, 54, 56, and 58. The dozers 200 inzones 50, 54, and 58 drive the overburden 29L to a staging area 59,where the dozers 200 operating in areas 52 and 56 take turns dozing theoverburden 29L through the staging area 59 into the chute 40 to theapron feeder 150. The dozers 200 in zones 50, 54, and 58 preferablyadvance while the dozers in zones 52 and 56 retreat and vice versa toprovide a system of continuous operation for all of the dozers.

FIG. 10 shows a second embodiment for dozing loosened overburden 29L ina section S₁ into the apron feeder 150, in which the dozers 200 in zones52 and 56 doze the overburden 29 to the staging area 59 and dozers 200in zones 50, 54 and 58 doze the overburden down the chute 40 to theapron feeder 150. Again, the dozers 200 in zones 50, 54, and 58preferably advance while the dozers in zones 52 and 56 retreat and viceversa to provide a system of continuous operation for all of the dozers.

FIG. 11 shows a third embodiment for dozing loosened overburden 29L in asection S₁ into the apron feeder 150, in which the dozers 200 in zones61 and 63 feed overburden 29L to dozers 200 in zones 60, 62, 64, and 66.The dozers 200 in zones 60, 62, 64, and 66 in turn feed overburden 29Linto a slot 69. Another dozer 200 then dozes all of the overburden 29Lin the slot 69 down the chute 40 to the apron feeder 150. The thirdembodiment's advantage is that it allows for more dozers 200 to work inconcert with each other over a wider mining area 36. Further, becauseonly the dozer 200 in the slot 69 feeds the apron feeder 150, there islittle chance of a traffic jam at the slot 69.

FIGS. 12A-H illustrate iterative steps of a fourth embodiment for dozingloosened overburden 29L in a section S₁ to the apron feeder 150. Thisembodiment uses five dozers, one in each of four zones 70, 72, 74, and76 and the fifth in a slot 75 to feed overburden 29L to the chute 40 anddown to the apron feeder 150. The apron feeder 150 is illustratedloading dump trucks 180. Each truck 180 leaves the area once it is fullof overburden 29L, and another takes its place.

In the step shown in FIG. 12A, all dozers advance towards the slot 75,with the dozer 200 in zone 70 arriving in the slot 75 first, where itdumps its load of overburden. In the step in FIG. 12B, the dozer 200 inzone 70 begins its retreat through its zone 70 to gather another load,and the dozer 200 in the slot 75 prepares to drive a load to the hopper40. The other dozers in the zones 72, 74, and 76 advance. In FIG. 12C,the dozer 200 in zone 74 has dumped its load of overburden and beginsits run to pick up more overburden. The dozer 200 in zone 70 continuesits run to pick up overburden, while the dozers in zones 72 and 76advance.

In FIG. 12D, the dozers in zones 70 and 76 advance and the dozers inzones 72 and 74 are still returning to pick up overburden. In FIG. 12E,the dozers in zones 70, 74, and 76 advance while the dozer 200 in zone72, having dumped its load of overburden, returns to pick up moreoverburden. In FIG. 12F, the dozer 200 in zone 76 has dumped itsoverburden, and returns to pick up overburden, while the dozers in zones70, 72, and 74 advance.

In FIG. 12G, the dozer 200 in zone 76 retreats, while the othersadvance. Finally, in FIG. 12H, the dozer 200 in zone 70 has dumped itsload and returns for another, while the other dozers in zones 72, 74,and 76 advance. During these various advances through the zones, thedozer 200 in the slot 75 moves back and forth, driving the dumped loadsinto the natural hopper 40, with all dozers taking care not to interferewith one another and cause any work stoppage.

FIGS. 13A-H illustrate iterative steps of a fifth embodiment for dozingloosened overburden 29L in a section S₁ to the apron feeder 150. Thisembodiment uses four dozers, one in each of three zones 80, 82 and 84and the fourth in a slot 85 to feed the natural hopper 40 leading to theapron feeder 150. The apron feeder 150 is illustrated loading dumptrucks 180. Each truck 180 leaves the area once it is full of overburden29L, and another takes its place.

The consecutive steps of dozer movements are shown FIGS. 13A-H. FIG. 13Ashows the dozers 200 in zones 80, 82, and 84 advancing to the slot 85,and FIG. 13B shows the same dozers further advanced towards the slot 85.In FIG. 13C, the dozer 200 in zone 80 has dumped its load of overburdenand is beginning its return for another load, while the dozers in zones82 and 84 advance towards the slot 85. In FIG. 13D, the dozer 200 inzone 82 begins its return for another load following the dumping of aload into the slot 85, while the dozer 200 in zone 80 continues itsreturn run, and the dozer 200 in zone 84 advances.

In FIG. 13E, the dozers in zones 80 and 84 advance, while the dozer 200in zone 82 retreats for another load of overburden. In FIG. 13F, thedozers in zones 80, 82 advance, while the dozer 200 in zone 84 beginsits return for another load, having just dumped its load in the slot 85,and FIG. 13G shows the further advance of the dozers following the stepshown in FIG. 13F. Finally, FIG. 13H shows the dozers in zones 82 and 84advance while the dozer 200 in zone 80 retreats to get another load ofoverburden, having just dumped its own load.

During these various advances through the zones, the dozer 200 in theslot 85 moves back and forth, driving the dumped loads into the naturalhopper 40, with all dozers 200 taking care not to interfere with eachother.

The various methods can be used in a single mining site. In addition,variants thereof may be used that employ more or less dozers 200. Forexample if one or more zones has a deeper cut of overburden 29 toremove, it may be advantageous to position more than one dozer in thatzone, or split the zone into subzones. If too much overburdenaccumulates in a single dozer slot, and the dozer 200 therein fallsbehind, a staging area for two or more dozers may be more efficientlyemployed.

Apron Feeder Relocation

Once the dozers 200 remove the overburden from a section S₁, the apronfeeder 150 is then moved to a new location, such as adjacent the nextsection of loosened overburden S₂. FIGS. 14A-I illustrate a preferredsequential procedure for moving the apron feeder 150 after theoverburden removal operation is completed from section S₁.

As the dozers 200 are completing the dozing of the lowest layer of theoverburden 29L of a section S₁ into the apron feeder 150 (FIG. 14A), asingle dozer 200 or other equipment cleans out overburden spillage onthe right hand side of the apron feeder until it is clear as shown inFIG. 14B.

Once the right hand side of the apron 150 is clear, a dozer 200 or otherequipment removes the right hand wall 170 of the apron feeder 150. Withthe right hand wall 170 removed, a dozer 200 or other equipment removesfurther overburden spillage, FIG. 14C, to completely clear right handside of the apron feeder.

A dozer 200 then cleans away any overburden spillage about the left handwall 172 and removes the wall 172 as shown in FIG. 14D. Any remainingoverburden spillage 89 adjacent the hydraulic housing 174 on the leftside is then also removed as shown in FIG. 14E. Thereafter, thehydraulic housing 174 is disconnected from the apron feeder 150, and adozer 200 removes the housing 174 for final cleaning on the left handside, as shown in FIG. 14F. Finally, as shown in sequential steps 14G-Ia transporter 190 moves in from the right of the apron feeder, lifts itand carries the apron feeder 150 to its new location, such as adjacentanother section S₂ of loosened overburden whereat the hydraulic housing174 and walls 170, 172 are reattached.

While specific embodiments of the invention are disclosed they are notlimiting in nature. Those of ordinary skill in the art will recognize avariety of variations in parameters, equipment and processes which canbe employed within the scope of the invention.

1. An apron feeder comprising: a plurality of transport flightsconfigured for travel in a continuous elongated loop having top andbottom sides and configured to convey materials on the top side from afeed end to an outlet end of the apron feeder; a scroll element mountedat the feed end of the apron feeder configured to catch materialspilling off in front of the feed end, said scroll element having anelongated flat portion extending beneath a portion of the bottom side ofthe loop of transport flights in a substantially parallel orientation; awiper element mounted on a transport flight configured to clean materialcaught by the scroll element as the wiper element moves from the bottomside to the top side of the loop with the flight to which the wiperelement is mounted; and a grizzly element mounted on a transport flightto break apart material caught on the scroll element before the wiperelement cleans the material from the scroll element.
 2. The apron feederof claim 1, wherein: the grizzly element comprises a row of metal teethspanning transversely across the flight on which the grizzly element ismounted; and the wiper element comprises a raised blade spanningtransversely across the flight on which the wiper element is mounted. 3.The apron feeder of claim 1, wherein a plurality of grizzly and wiperelement sets are provided evenly spaced along loop of flights.
 4. Theapron feeder of claim 1 wherein: the feed end and the outlet end definea conveying direction; the apron feeder is mounted on a frame at adesired fixed angular orientation with the feed end at a lower loadposition and the outlet end at a raised position; and the frame has anopen area thereunder to receive a transport unit to transport the apronfeeder in its fixed angular orientation in a direction transverse to theconveying direction of the apron feeder when the transport unit ispositioned beneath the center of gravity of the apron feeder assembly.5. The apron feeder of claim 4 further comprising a transport unit thatincludes a vertically displaceable member for lifting the apron feederin advance of transporting it.
 6. The apron feeder assembly of claim 5wherein the transport unit is attached to the apron feeder frame.
 7. Theapron feeder assembly of claim 5 wherein the transport unit includesmotive means for imparting movement in the transverse direction and arotation assembly for reorienting the motive means with respect to theapron feeder to enable the apron feeder to be transported in a directionaligned with the conveying direction.
 8. The apron feeder assemblyaccording to claim 5 wherein the transport unit includes treads forimparting movement in the transverse direction.